Bimetal: materials made from two bonded metals

Characteristics and construction

Bimetal pieces typically consist of two thin strips, plates or bonded layers. Joining methods include rolling, welding, brazing and adhesive bonding; clad metal produced by roll bonding is a common industrial technique. The choice of metals depends on the desired combination of properties such as strength, corrosion resistance, conductivity, color, weight and, importantly for thermal devices, coefficients of thermal expansion.

How bimetals work

When the component is heated or cooled, the two metals expand or contract by different amounts. If they are constrained together, this mismatch causes the combined element to bend, curl or generate stress and force. That predictable mechanical motion is widely used as a simple, reliable actuator or sensor without requiring electrical power for the movement itself.

Common applications

• Temperature control: bimetallic strips are used as on/off switches or regulators in thermostats, irons, and electric kettles.
• Electrical protection: some circuit breakers and thermal cutouts use bimetal elements to open a circuit when overheated.
• Timekeeping and valves: older clock escapements and some mechanical valves use bimetal compensation for temperature drift.
• Coins and decoration: bimetallic coins combine two metals for security and appearance; architectural or decorative items exploit contrasting finishes.

Advantages, limits and distinctions

Advantages include simplicity, low cost, passive operation and clear mechanical response to temperature changes. Limitations are slower response than electronic sensors, finite fatigue life from repeated bending, and a limited range of motion. It is important to distinguish bimetal objects from alloys and from layered composites; bimetals keep distinct layers, whereas alloys mix elements atomically.

History and notable facts

Bimetallic technology has long been used wherever a durable, purely mechanical temperature response is required. It was developed and refined alongside industrial manufacturing techniques that allowed reliable bonding of dissimilar metals. Today bimetallic components remain common in household appliances and industrial controls because of their robustness and predictable behavior.

For more technical descriptions and manufacturing details, see manufacturing notes, practical applications at application summaries and comparative material data at material references.